Easily transportable devices with wireless telecommunications capabilities, such as mobile telephones, personal digital assistants, handheld computers, and similar devices, will be referred to herein as user equipment (UE). A communications connection between two UEs can be referred to as a call or a session.
As telecommunications technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an enhanced node B (ENB) rather than a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment.
In traditional wireless telecommunications systems, transmission equipment in a base station transmits signals throughout a geographic region known as a cell. For LTE and other advanced equipment, the region in which a UE can gain access to a telecommunications network might be referred to by a different name, such as a hot spot. The term “cell” will be used herein to refer to any region in which a UE can gain access to a telecommunications network, regardless of the type of UE and regardless of whether the region is a traditional cell, a region served by LTE equipment such as an ENB, or some other region or location in which wireless telecommunications services are available.
Some UEs communicate in a circuit switched mode, wherein a dedicated communication path exists between two devices. For the duration of a call or session, all data exchanged between the two devices travels along the single path. Some UEs have the capability to communicate in a packet switched mode. In packet switching, a data stream representing a portion of a call or session is divided into packets that are given unique identifiers. The packets might then be transmitted from a source to a destination along different paths and might arrive at the destination at different times. Upon reaching the destination, the packets are reassembled into their original sequence based on the identifiers. Communications that take place via circuit switching can be said to occur in the circuit switched domain and communications that take place via packet switching can be said to occur in the packet switched domain.
Different UEs might use different types of radio access technology (RAT) to access a telecommunications network. Some UEs, which can be referred to as multi-domain UEs or multi-mode UEs, are capable of communicating using more than one RAT. Examples of RATs or of network technologies that might use different types of RATs include Code Division Multiple Access 2000 (CDMA2000), UTRAN (UTMS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network), Global System for Mobile Communications (GSM), GSM EDGE Radio Access Network (GERAN), Generic Access Network (GAN), Wireless Local Area Network (WLAN), General Packet Radio Service (GPRS), Worldwide Interoperability for Microwave Access (WiMAX), 1× Evolution-Data Optimized (1× EV-DO), High-Speed Downlink Packet Access (HSDPA), Digital Enhanced Cordless Technology (DECT), and High Rate Packet Data (HRPD). Other RATs or other network technologies based on these RATs may be familiar to one of skill in the art.